Laser-induced transverse voltage in (111)-oriented TiO1+δ epitaxial thin films with cubic structure

Abstract

The laser-induced transverse voltage (LITV) was investigated systematically in (111)-oriented cubic TiO1+δ (1.08 ≤ 1 + δ ≤ 1.28) thin films grown on nontilted (0001)-oriented α-Al2O3 substrates. Utilizing the anisotropy between [001] and [110] directions, a feasible LITV measuring configuration was designed, and the peak voltage Up at room temperature reaches 0.92 V for the sample TiO1.08 irradiated by a laser with a wavelength of ∼248 nm and an energy density of ∼10 mJ/cm2. Both the voltage amplitude and the sensitivity of LITV decrease with the increasing oxygen content, probably due to the enhancement of disorder strength and the reduction of density of electronic states near the Fermi level. The Up value of the TiO1.08 film rises to 1.22 V upon increasing temperature to 450 K and then decreases upon further increasing the temperature. The LITV variations at different wavelengths indicate that the LITV should mainly come from a transverse thermoelectric effect when the photon energy is lower than the bandgap but may contain a contribution from a transverse photovoltaic effect when the photon energy is larger than the bandgap. These results provide considerable insight into LITV and offer a feasible method to explore more LITV materials.